1. Field of the Invention
The present invention relates to a plasma processing apparatus which gives plasma processing to a processed object with using high frequency energy such as a microwave, and in particular, to a plasma processing apparatus equipped with a window permeated by high frequency energy, a plasma processing method, a dielectric for a permeable window used therefor, and a production method of a structure where the dielectric for a permeable window is used.
2. Related Background Art
As a plasma processing apparatus using high frequency energy such as a microwave and a VHF wave as an excitation source for plasma excitation, a plasma polymerization apparatus, a CVD apparatus, a surface treatment apparatus, an etching apparatus, an ashing apparatus, a cleaning apparatus, etc. are known.
To cite a case of a microwave as an example, CVD using such a so-called microwave plasma processing apparatus is performed as follows.
That is, a gas is introduced into a plasma-generating chamber and/or a film-forming chamber of microwave plasma CVD apparatus, and microwave energy is supplied simultaneously to generate plasma in the plasma generation chamber. Furthermore, the gas is excited, dissociated, and ionized, and the like to generate ions, radicals, etc., and a deposition film is formed on the processed object arranged in the plasma generation chamber or the film formation chamber distant from the plasma generation chamber. In addition, surface treatment such as plasma polymerization, oxidization, nitriding, and fluoridation of an organic substance can be also performed by the same technique.
Moreover, the etching processing of the processed object using the so-called microwave plasma etching apparatus is performed, for example, as follows. That is, an etching gas is introduced into the processing chamber of this apparatus, and microwave energy is supplied simultaneously to generate plasma in this processing chamber. In addition, the etching gas is excited, dissociated and ionized to etch a surface of the processed object arranged in this processing chamber by the ions, radicals, etc. that are generated.
Moreover, the ashing processing of the processed object that uses a so-called microwave plasma-ashing apparatus is performed, for example, as follows. That is, an ashing gas is introduced into the processing chamber of this apparatus, and microwave energy is supplied simultaneously to generate plasma in this processing chamber. In addition, the ashing gas is excited, dissociated and ionized to ash a face of the processed object arranged in this processing chamber, that is, photo resist by the ions, radicals, and ozone etc. that are generated. Similarly to the ashing, it is possible to perform cleaning for removing an undesired substance adhering to the processed face of the processed object.
In a microwave plasma processing apparatus, since a microwave is used as a source of gas excitation, electrons can be accelerated by an electric field at a high frequency, and hence gas molecules can be ionized and excited efficiently. So, since having high gas ionization efficiency, excitation efficiency, and dissociation efficiency, the microwave plasma processing apparatus has such advantages that it is possible to form high-density plasma comparatively easily and that it is possible to perform quality processing at high speed and low temperature. Moreover, the apparatus also has such advantages that, since a microwave permeates a dielectric like silica glass, the plasma processing apparatus can be constituted as an electrodeless discharge type apparatus and that, owing to this, highly clean plasma processing can be performed.
In order to further accelerate such a microwave plasma processing apparatus, a plasma processing apparatus using electron cyclotron resonance (ECR) has also been put in practical use. The ECR is a phenomenon in which, when flux density is 87.5 mT, an electronic cyclotron frequency that is a frequency of electrons revolving around lines of magnetic force meets a common microwave frequency of 2.45 GHz, the electrons absorbs microwaves resonantly to be accelerated, and high-density plasma is generated.
Moreover, another type of plasma processing apparatus for high-density plasma generation is also proposed.
For example, plasma-processing apparatuses each using a radial line slot antenna (RLSA) are disclosed in Japanese Patent Application Laid-Open No. 03-262119, Japanese Patent Application Laid-Open No. 01-184923, and the specification of U.S. Pat. No. 5,034,086.
Alternatively, plasma processing apparatuses each using a circular wave guide with termination are disclosed in Japanese Patent Application Laid-Open No. 05-290995, the specification of U.S. Pat. No. 5,359,177, and EPO564359 bulletin.
Apart from these, as examples of microwave plasma processing apparatuses in recent years, apparatuses each using a circular wave guide without termination where a plurality of slots is formed in the inside thereof are proposed as apparatuses of uniformly and effectively introducing microwaves (Japanese Patent Application Laid-Open No. 5-345982 and U.S. Pat. No. 5,538,699).
On the other hand, a plasma processing apparatus using a disk-like microwave introduction apparatus is disclosed in Japanese Patent Application Laid-Open No. 7-90591. This apparatus introduces a gas into a wave guide, and discharges the gas toward a plasma generation chamber from slots provided in the wave guide.
Moreover, a plasma processing apparatus equipped with a circular (annular) wave guide is also disclosed in Japanese Patent Application Laid-Open No. 11-40397.
On the other hand, FIGS. 9 to 12 are schematic diagrams showing an example of a conventional plasma processing apparatus.
FIG. 9 shows a container 1 whose inside can be exhausted, supporting means 2 for a processed object, a microwave source 3 consisting of a circular wave guide having a circular wave guide therein, a dielectric window 4, and a gas supply pipe 7 having a gas supply port 7a. An apparatus assembled from these parts introduces a microwave from the microwave introduction port 15 of the microwave source 3 to supply the microwave from the slots 3b to the container 1 through the dielectric window 4.
FIGS. 10 to 12 are schematic diagrams for explaining the propagation of a microwave in a circular wave guide of the microwave source, and the situation of radiation of the microwaves from the slots.
FIG. 10 shows the situation at the time of seeing the circular wave guide from the above with omitting the slots. FIG. 11 shows a cross section taken on line 11xe2x80x9411 in FIG. 10, and FIG. 12 shows a cross section taken on line 12xe2x80x9412.
Since the vicinity of the microwave introduction port 15 serves as an equivalent circuit of E-plane T-junction, the microwave introduced from the microwave introduction port 15 is changed on its course in a clockwise direction d2 and a counterclockwise direction d1. Since each slot 3b is provided so as to intersect with the proceeding directions d1 and d2 of the microwave, the microwave proceeds with emitting microwaves from the slots.
Since the circular wave guide is without termination, the microwaves propagating in the directions d1 and d2 (z-axis direction) interfere with each other. It becomes easy to generate a standing wave in a desired mode by making the length of a ring C1 formed by connecting centers of the wave guide, that is, circumference be an integral multiple of a guide wavelength (wavelength in the guide).
FIG. 11 shows a cross section perpendicular to a proceeding direction (z-axis orientation) of the microwave, and upper and lower faces 3c of the wave guide are H-plane perpendicular to the direction of an electric field EF. In addition, left and right faces 3d of the wave guide are E-plane parallel to the direction of the electric field EF. Reference symbol C0 denotes a center in the longitudinal direction of the slot 3b, i.e., the direction (x-axis direction) perpendicular to the proceeding direction and propagating direction of the microwave.
Thus, the cross section of the wave guide, which is perpendicular to the microwave proceeding direction, is a rectangle cross section whose long side and short side are the x-axis and the y-axis respectively.
A microwave MW introduced in the circular wave guide 3a is divided into the right and left by an E-plane T-junction distribution block 10, and propagates at guide wavelength longer than that in a free space. The distributed microwaves interfere with each other in facing sections, and hence generate a standing wave every half of the guide wavelength. A leakage wave EW emitted through the dielectric window 4 from the slot 3b provided in a position where the electric field crossing the slot becomes the maximum generates plasma P1 near the slot 3b. When an electronic frequency of the generated plasma P1 exceeds a frequency of a microwave power supply (when, for example, a frequency of the power supply is 2.45 GHz, electron density exceeds 7xc3x971010 cmxe2x88x923), the microwave cannot propagate in the plasma, that is, cut-off arises. The microwave propagates on the boundary between the dielectric window 4 and plasma as a surface wave SW. Surface waves SW introduced from adjoining slots interfere with each other, and a loop of an electric field is produced every half the wavelength of the surface wave SW (xcexxc2x7xcex5xcex3xe2x88x92xc2xd [xcex: free space microwave wavelength; xcex5xcex3: dielectric constant]). This loop electric field caused by the interference of surface waves leaking out to the plasma generating space side 1 generates surface-wave interfered plasma (SIP) P2. If a process gas is introduced into the plasma processing chamber at this time, the process gas is excited, dissociated, and ionized by the high-density plasma generated, and can process the face of the processed object.
Such a microwave plasma processing apparatus can generates high-density low-electron temperature plasma having electron density of 1012/cm3 or more, electron temperature of 3 eV or less, and plasma potential is 20 V or less within the uniformity of xc2x13% in a space where pressure is about 1.33 Pa, microwave power is 1 kW or more, and its diameter is 300 mm or more.
Therefore, it is possible to supply the gas to the processed object in an active condition by fully reacting the gas.
In addition, when pressure is 2.7xc3x97103 Pa and microwave power is 2 kW, it becomes impossible to detect current caused by the plasma in the position over 50 mm apart from the internal surface of the dielectric window. This means that a layer of very thin plasma is made near the dielectric window in the high pressure area in which plasma diffusion is suppressed. Therefore, since the surface damage of a substrate by incident ions also decreases, high-quality and high-speed processing becomes possible even at low temperature.
In plasma processing apparatus, quartz glass (silicon oxide), alumina (aluminum oxide), aluminum nitride, or the like is used as a dielectric window without being dependent on the configuration of a microwave source.
However, quartz glass is easily vulnerable by a gas with fluorine content like C4F8 used for etching, etc.
Although the dielectric constant of alumina is higher than that of quartz and is also superior in the durability over a gas with fluorine content, its thermal conductivity is low and coefficient of thermal expansion is high. Hence alumina is comparatively easy to be broken by ion incidence from plasma.
Although there is no problem like alumina in an aluminum nitride, the transmissivity of a microwave might lower gradually with the time and plasma-processing speed might become low.
As described above, it is not sufficient for providing a superior plasma processing apparatus just to choose the material constituting a dielectric window.
An object of the present invention is to provide a plasma processing apparatus, a plasma processing method, and a dielectric for a permeable window that make processing speed hardly lowered.
Another object of the present invention is to provide a production method of a structure in which plasma processing is performed with using a reliable plasma processing apparatus and which is excellent in repeatability.
The main point of a plasma processing apparatus according to the present invention is characterized in that, in the plasma processing apparatus that has a container a gas supply port that supplies a process gas in the above-described container and a permeable window permeating high frequency energy for generating the plasma of the gas, a light shielding film for shielding the window from light, which may increase dielectric loss of a permeable window, is provided on the internal surface of the window.
The main point of another plasma processing apparatus according to the present invention is characterized in that.
In the plasma processing apparatus that has a container a gas supply port that supplies a process gas in the above-described container and a reflective film that reflects incident light, which may increase the dielectric loss of a permeable window, on the internal surface of the permeable window permeating microwave energy for generating the plasma of the above-described gas.
The main point of still another plasma processing apparatus according to the present invention is characterized in that, in the plasma processing apparatus that has a container a gas supply port that supplies a process gas in the above-described container and an optical absorption film that absorbs incident light, which may increase the dielectric loss of a permeable window, on the internal surface of a microwave permeable window permeating microwave energy for generating the plasma of the above-described gas.
Furthermore, the main point of a dielectric for a permeable window according to the present invention is characterized in that a light shielding film for shielding the window from light that may increase the dielectric loss is provided on at least one surface thereof.
The main point of another dielectric for a permeable window according to the present invention is characterized in that a reflective film reflecting light that may increase dielectric loss is provided on at least one surface thereof.
The main point of still another dielectric for a permeable window according to the present invention is characterized in that an optical absorption film absorbing light, which may increase dielectric loss, is provided on at least one surface thereof.
With citing an example at the time of using aluminum nitride for a dielectric window, an action of the light shielding film that can be used in the present invention will be described.
For example, a mechanism of dielectric loss (tanxcex4) arising in a microwave wavelength region of aluminum nitride is considered to be that pairs of impurity, which is replaced from nitrogen, and an aluminum vacancy are formed in an aluminum nitride crystal, and impurity oxygen ionized vibrates with response to an external electric field.
Although an ionization rate by oxygen heated at several hundred degrees centigrade is not so high, an ionization rate by light at 2.0 eV to 2.8 eV (this is equivalent to 440 nm to 600 nm) is high.
Moreover, the radiation within the above-described wavelength range is found in the plasma used for plasma processing.
Therefore, it is considerable that impurity oxygen is ionized by the strong light emitted from high-density plasma by the microwave permeable window made from aluminum nitride, and dielectric loss increases. Probably, there may be some materials besides aluminum nitride where dielectric loss arises by the similar mechanism.
According to the present invention, by providing a light shielding film that disturbs the incidence of light, causing the increase of dielectric loss, into a permeable window, it becomes possible to suppress the dielectric loss caused by the permeable window and the time-dependent degradation of processing speed.
As a light shielding film used in the present invention, a film can be cited, the film which can reduce the amount of incidence of light causing the increase of dielectric loss in a permeable window among the plasma light which is incident to the permeable dielectric window made of aluminum nitride or the like. In more detail, what is preferably used is an optical absorption film that may absorb the light that becomes a cause of increasing the dielectric loss, a reflective film that may reflect the light being the cause of increasing the dielectric loss, or the combination of the above-mentioned optical absorption film and the above-mentioned reflective film.